Cavity wall / security bolt fixings

wersal gummage

Hi folks,

I'd like to install a few decent security anchor points on walls in my shed. However, I have a cavity block shed so not sure it's possible.

Most of the decent anchor points I'm looking at are based on a system of 4 fixing points, involving a 16mm sds bit drilling to about 60 to 90mm, then hammering in the expanding concrete fixing bolts, then bolting the anchor to the fixings and hammering ball-bearings into the bolt heads....

I guess a cavity block is 30mm or 40mm before hitting air? So I can't do this basically?

This is more of a peace of mind thing than a pressing security issue, shed is alarmed, I a fairly secure location etc. I know an alternative is to go into the floor, I'm not sure how deep the slab is that shed sits on, but also I have items already wall mounted up high in shed and don't want to try find chains long enough to reach a ground anchor.

Thanks for any comments or advice

10-10-20

Not sure what you mean by "hammering ball-bearings into the bolt heads" but:

These anchors are fine for where you hit the void on cavity blocks:

https://www.masonryfixings.ie/hm-ss-8mm-x-54mm-metal-cavity-fixing-with-hexagon-head--box-50

They do have a slight habit of turning in the void before they are set, but I'd use those in the voids and then a rawlbolt where you hit solid block.

https://www.screwfix.ie/c/screws-nails-fixings/shield-anchors/cat840080

wersal gummage

Thanks.

What I'm talking about is essentially a security device, like a large sort of eye bolt (or anchor) in a wall or concrete, which you would put a chain through. I've tried to attach a photo below, which actually appears to show the device in a cavity block but maybe they poured it with concrete inside.

So you'd drill your holes in the wall, install the fixings, then place your bolts through the anchor plate and screw into the fixings. However, that's no good as a security device because anyone can unscrew the bolts from the fixings, taking the chain and whatever you have secured. So the bolts are typically Allen /hex heads and are supplied with ball bearings which you drive into the Allen /hex head with a hammer, in theory preventing anyone from removing the bolts.

These anchor type devices are all supplied with their own fixings and bolts etc, and they all appear to require a 16mm hole drilled (x4), to about 60 to 90mm deep depending on different models.

I had a look at those fixings you linked, thanks but I think they are probably not going to be big enough for a 16mm hole.

What I'm trying to do is really designed to go into concrete and just wondering are there any workarounds with cavity.

wersal gummage

This picture probably shows it better as the black plastic bit is just a cover not really doing anything

10-10-20

Get you. What if you used an angle grinder and a concrete blade to open and expose some of the cavity and then backfilled the cavity with concrete. Shouldn't be too difficult of a job.

Dr_Colossus

Was going to suggest similar to 10-10-20 above, after drilling the four 16mm holes could use them to pump in some filler and leave to set before drilling again and installing the bolts. Not sure what to use for filler though that's easily available in a tube and strong once set. Concrete will be difficult through such small holes but maybe some fine sand/cement with some plasticiser might be easier.

Ginger83

I agree with 10-10-20 but I would also say the floor slab should be thicker.

Gen.Zhukov

My goto with cavity blocks is the mortar between the ends of the blocks - In this case I'd get a steel plate (as pic) and fix the anchor to the vertical plate (before or after bolting the plate to wall - whatever suits)

Lumen

You can buy the hammer-a-ball-bearing-in security bolts/anchors separately from the wall anchors. You just need to know the diameter (M8/M10/M12 or whatever) and the length, and then find a supplier that stocks them.

e.g. https://www.sheffarc.com/products/anti-theft-countersunk-dome-head-security-bolts-fixings-m8-m10-for-masonry-brick

There are other sorts of removable anchors e.g. pin torx head or curly shaped ones.

I don't know anything about limitations of fixing into cavity blocks though.

wersal gummage

Thanks Lumen,

My concern, including with those bolts, is that they are over 6cm long and designed to be secured into concrete or at least something solid. I think they expand and strengthen their hold by expanding.

The cavity block is probably 3cm before it hits a hollow, so I imagine that the expanding nature and overall security of these types of fixings is massively reduced by fitting them to cavity.

To be honest, I hadn't even thought about it really but one of the Oxford products had quite clearly in the description not to fit to a cavity wall and it is using the same basic idea as all other products.

I'm not really inclined to start opening up the blocks and pump cement in, gett a bit beyond my comfort levels, I'd also been planning to mount the thing about 7 or 8 feet off the ground so it wouldn't be a case of just filling one block, I presume anything pumped would flow to the bottom and I'd have to fill the whole wall.

10-10-20

https://www.boards.ie/discussion/comment/121158558#Comment_121158558

Nah, I'd drop a rock into the gap to catch on the cavity-lip and then back-fill the void with concrete. If not a rock, some loose-fill stone would do. BUt yes, not everybody's cup of tea, I can understand that.

wersal gummage

https://www.boards.ie/discussion/comment/121158672#Comment_121158672

Thanks, not doubting your suggestion I just meant it's getting a bit beyond the level of work I'm looking to do...

Google tells me not to drill into the mortar between blocks to fix things to, I know a lot of what's on there is US based. Does same apply here?

GreeBo

Do you have a concrete floor that you could use instead?

10-10-20

https://www.boards.ie/discussion/comment/121171955#Comment_121171955

Yes, the mortar is the weakest point and using an expanding anchor in a mortar joint will only separate the blocks.

wersal gummage

https://www.boards.ie/discussion/comment/121172020#Comment_121172020

Yes but as mentioned, I'm trying to secure something at about 7 or 8 feet height on a wall, so a ground anchor would require a fairly ridiculous (and expensive) chain... I already have a few high quality chains but they are only maybe 1.5m or something like that. But yeah, it may be the best option I accept that it's just far from ideal.

My second issue is I'm not aware of the dept of the floor and wouldn't be confident it is 10cm deep, so could end up drilling into ground below... Also would there be any issues drilling through DPM in floor?

Thanks for all the comments

loyatemu

there's a huge array of fittings for hanging stuff on plasterboard, and some good youtube videos comparing them. I'd imagine some of them would be suitable for using on hollow block too as the basic principle is the same (I'm not sure of the relative thicknesses).

Gen.Zhukov

I've put wall anchors in the mortar lots of times with no issues - my 1st drawing above has 6 fitted so they don't need to be massive...

but anyway...

There is another variation of that steel plate idea. 2 long cup square bolts and nuts (coach bolts) going through the wall with the dome bolt head and washer on the outside and the threaded end coming through the wall - The plate, with the anchor already fitted and 2 mounting holes drilled in it, then fits onto the 2 threaded bolts and tightened up with nuts - Then depending on your kit (personally I'd weld the nut to the bolt) the easiest way is to drill a hole through the nut and bolt and ram a pin into that hole meaning the nut cannot be undone - I've gone through the mortar again because you have the strength of the block ends there for compression and it will make feeding the bolt through easier

You don't have to use coach bolts (hex would do) it's just the dome head will look slightly better on the outside

Oh and btw, the ball bearing thing is just one way of ensuring the bolts can't be removed...drilling out the hex socket is another

GreeBo

https://www.boards.ie/discussion/comment/121158558#Comment_121158558

RE: filling the cavity, you really only need to fill the block you are fixing to, so you can drill some holes in the 2 blocks below and use expanding foam to fill them. Then knock a hole in the block above and pour in a runny mix. In a day or two you can just bolt as normal?

Or just knock the face off the brick you want to fix to and above, use something flat as shuttering and fill the void with a less runny mix.

When you take the face off you can use foam etc to ensure that your concrete mix won't just flow into the cavities below.

wersal gummage

Thanks for all the comments, much appreciated.

Looking like I'll need to do a bit more work than I had intended.

Before I do that, I had one last thought.

I had intended to use a 4 bolt design anchor, but there are anchors with 2 bolts. I understand they'd be less secure.

But could I fix a 2 bolt anchor to the part of the block that is solid, eg the very edge of the block? Say like this? Would there be enough block at the edge to go into with a 16mm bit?

I know filling the cavity is a better job

GreeBo

I'd worry about blowing out the block with this approach tbh. These blocks are great in compression but not great when you are drilling into them with a large diameter hammer drill or when you tighten any type of expanding fitting.

Even drilling into the hollow part will often leave a much bigger hole in the back compared to the front (it can blow out easily)

Lumen

I like the through bolt approach as it leaves your cavity intact.